1. Field of the Invention
The present invention relates to a manufacturing method for shielded flat electrical cable.
2. Background Art
Conventionally, thin flexible flat cable has been widely used in applications such as the cable connecting the printed circuit boards of electronic apparatuses. FIG. 1 shows an example of such conventional flat cable. Reference numerals 2 and 4 indicate conductors, both of which have rectangular cross sections and are formed of flexible metal. These conductors 2 and 4 are formed with standardized dimensions and of standardized materials and are arranged in a parallel fashion with a standard spacing therebetween. Furthermore, of theses conductors, conductors 2 are used as signal transmission lines, while conductor 4 is used as a grounding line. These conductors 2 and 4 are covered by means of an insulation cladding 6 comprising a resin having an electric insulation capacity. Insulation cladding 6 is formed around conductors 2 and 4 by the extrusion cladding of the resin in a heat-melted state.
There are cases in which this flat cable may need to be shielded from outside electromagnetic induction, or electrostatic induction, and to avoid the leakage of signals, depending on the conditions of use. In such a case, flat shielded cable is used which is provided with a shield layer 8 which is formed around insulation cladding 6 of the flat cables and comprises metal foil, a resin sheet to which metal has been laminated, or a metal wire grid (FIG. 2 shows an example of such a flat cable).
In such flat shielded cable, it is desirable to electrically connect the shield layer with the grounding line (conductor) 4 and thus equalize the electric potential thereof. In order to do this, the shield layer 8 is connected to grounding line (conductor) 4 at the end part thereof; however, if connection is made at the end part alone, cutting at this point of connection, or at an intermediate position along the shield layer, would cause the connection between the shield layer and the grounding line to be cut so that the shield effectiveness as a whole would be lost.
As a means to increase the reliability of the shield, it has been considered to connect grounding line (conductor) 4 and the shield layer along the entire length of the cable; however, in order to do this, it is necessary to peel off insulation cladding 6 on the surface of grounding line (conductor) 4.
However, an appropriate technique for the effective removal of insulation cladding 6 from the surface of grounding line 4, without affecting the surrounding insulation cladding 6 covering signal lines (conductors) 2 has not been known.
Furthermore, a further type of flat wire is known, in which, as shown in FIG. 3, there is a construction such that conductors 2 and 4 are sandwiched between an upper and lower pair of insulation tapes 10; however, in flat cable with this construction as well, a technique for the effective removal of insulation tape 10 covering grounding line 4 has not been known.